Deflection coil system for colour television

ABSTRACT

A deflection coil system for colour television, comprising deflection coils which are subdivided into sections, an adjustable impedance being connected parallel to some of these sections for compensation of differences in the distribution of turns of the coils.

United States Patent [191 Dekeijser et al.

[ Nov. 26, 1974 1 DEFLECTION COIL SYSTEM FOR COLOUR TELEVISION [75] Inventors: Jacky Charles Dekeijser; Albert Jan Kuiper, both of Emmasingel, Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New

York, N.Y.

[22] Filed: Sept. 20, 1972 211 Appl. No; 290,651

[30] Foreign Application Priority Data Sept. 21, 1974 Netherlands 7112929 [52] US. Cl 315/27 XY, 335/213 [51] Int. Cl. Hfllj 29/70 [58] Field of Search 315/27 XY, 27 R; 335/213, 335/211, 210

[56] References Cited UNITED STATES PATENTS 2,228,821 l/l941 Hansen 315/27 XY 2,866,125 12/1958 Haantjes et al. 315/27 XY 3,169,207 2/1965 Obert et al.... 315/27 XY 3,456,149 7/1969 Van Mast 315/27 XY Primary Examiner-Maynard R. Wilbur Assistant Examiner-J. M. Potenza Attorney, Agent, or FirmFrank R. Trifari; Henry I. Steckler [57] ABSTRACT A deflection coil system for colour television, comprising deflection coils which are subdivided into sections, an adjustable impedance being connected parallel to some of these sections for compensation of differences in the distribution of turns of the coils.

10 Claims, 9 Drawing Figures PATENTEU m I914 3.851.215

saw no; 4

DEFLECTION COIL SYSTEM FOR COLOUR TELEVISION The invention relates to a deflection coil system for a colour television display tube, comprising deflection coils for electron beam deflection in the horizontal and the vertical direction, respectively, each coil consisting of a number of turns of a conductive wire, each of the coils for at least one of the two deflection directions being divided into a number of series-connected sections in that at least one turn which is situated between the first and the last turn of the coil is provided with a tapping.

Contemporary colour television display tubes usually comprise three electron guns which are preferably arranged at the comers of an equilateral triangle or are adjacently arranged on one line. Each of these electron guns generates an electron beam which, after having passed through one of the apertures in a shadow mask, impinges upon a phosphor dot on a rectangular display screen, the said phosphor dot thereby luminescing a given colour. By means of magnetic fields generated in a deflection coil system, the electron beams can be deflected such that they scan the entire display screen.

The dynamic convergence of the beams is of major importance in this respect. This means that, regardless of the angle through which the beams have been deflected, the three beams must always intersect each other at the area of the shadow mask so as to cause luminescence of the correct phosphor dots. This dynamic convergence greatly depends on the distribution of the turns of the wires constituting the deflection coils. During the manufacture of the coils, deviations occur in the turn distribution which cause a difference in the dynamic convergence in individual coil systems. Such differences are not acceptable, particularly in the case of colour television display tubes having large deflection angles.

A proposal has already been made for correcting such deviations, see US. Pat. No. 3,169,207. According to this proposal, each of the coils is woundwith a number of parallel wires, the coil being divided into a number of series-connected sections by means of tappings. The parallel wires of some of these sections are connected in parallel, and the parallel wires of other sections are connected in series. The effective turn distribution of the finished product can be influenced by varying the number of turns per section when the coil is being wound.

A drawback of this method is that the correction must be performed during winding, whilst the correction must also be rather coarse because a difference of at least one complete turn must each time be introduced. The invention has for its object to eliminate these drawbacks by providing a deflection coil system in which the effective turn distribution of the finished product can be changed while it has already been mounted on the display tube, arbitrarily small variations also being possible.

To this end a deflection coil system according to the invention is characterized in that at least one of the sections of each of the coils for at least one deflection direction is connected in parallel with a circuit of adjustable impedance.

One embodiment of the system according to the invention by means of which the convergence can be influenced on the entire display screen is characterized in that at least the first .or the last section of the relevant coils is provided with a parallel circuit.

For each winding of a deflection coil the angular distance a,, between this winding and the deflection direction can be determined. From this distance the angular distance 01,, of a mean turn can be calculated by means of the formula (cos u i-Ma) COS a (cos a )--'n(a) The invention will be described in detail with reference to the drawings, in which FIG. 1 is a perspective view of a saddle-shaped deflection coil which forms part of a. deflection coil system according to the invention,

FIG. 2 is a diagrammatic cross-sectional view of a ferromagnetic core having vertical saddle-shaped deflection coils,

FIG. 3 is a diagrammatic cross-sectional view of a ferromagnetic core having vertical toroidal deflection coils,

FIGS. 4 and 5 are diagrammatic views of two methods of dividing the coils of FIGS. 2. and 3 into sections in accordance with the invention, and

FIGS. 6a, 6b and 7a, 7b show a number of practical circuits for a deflection coil system according to the invention.

The saddle-shaped deflection coil shown in FIG. 1 is intended to be arranged on the outside of a display tube (not shown) so as to deflect an electron beam which is generated in the tube and whose direction of travel is denoted by an arrow 1. The coil consists of a number of turns of a conductive wire which. is composed of one or more strands, preferably copper wire, which enve lope a window 3. The coil comprises active parts 5 and 7 in which the wire extends mainly parallel to the direction of travel of the electrons, and a foremost coil end 9 and a rearmost coil end 11 where the wire extends substantially at right angles to the said direction of travel. The electrons are deflected substantially exclusively by the magnetic field which is generated in the active parts 5 and 7. The current required for the deflection can be supplied via connection wires 13 and 15 at the area of the rearmost coil end 11. Two turns are provided with tappings l7 and 19 that are also located at the rearmost coil end 11. As a result, the coil is divided into three sections, the first section consisting of the turns between the connection wire 13 and the first tapping 17, the second section consisting of the turns between the two tappings l7 and 19, and the third section consisting of the turns between thesecond tapping l9 and the connection wire 15. Connected in parallel to each of the three sections is a circuit 21 which has an adjustable impedance. Part of the deflection current which is applied to the coil via the supply wires 13 and 15 passes through a coil section while the remainder passes through the parallel circuit 21 which is associated with this section. If the impedance of the parallel circuit 21 is reduced, a larger part of the deflection current will pass through the parallel circuit. This has the same effect on the deflection of the electron beam as a reduction of the number of turns in the relevant section. In this manner continuous variation of the number of turns per section and hence of the turn distribution in the coil is possible.

FIG. 2 is a diagrammatic cross-sectional view of an angular ferromagnetic core 23 which .surrounds a pair of saddle-coils, only the active parts 5 and 7 and 5 and 7 thereof being visible in FIG. 2. The coils are arranged with respect to each other such that the connection line between the two windows 3 and 3' extends horizontally and intersects the axis of the core 23. The magnetic field which generates a current which flows through these coils causes a vertical deflection of an electron beam (not shown) travelling at right angles to the plane of the drawing. The deflection direction is denoted in the FIGS. 2 to 5 by a double arrow 25. For the deflection in the horizontal direction, a complete deflection coil system is also provided with a second pair of saddle coils (not shown for the sake of clarity), which are arranged to be coaxial with the first pair and which have been turned through an angle of 90 with respect to the first pair so that the connection line between the windows of the second coil pair extends in the vertical direction.

The effect'of themagnetic field which is generated by each turn of the coil on the deflection of the electrons is dependent on the location of this turn. This location is determined by measuring, in a plane perpendicular to the direction of travel of the electron beam, for example, the plane of the drawing in the FIGS. 2 to 5, the angle between the deflection direction of the coil on the one side and the connection line from the axis of the core 23 to the relevant turn on the other side.

FIG. 2 shows the angular distance a, of the turns which are arranged nearest to the deflection direction, and the angular distance a of the turns which are arranged furthest from the deflection direction.

The mean angular distance oz can be calculated from the angular distances of the turns by means of the formula:

Z, s ny-M cos a,=-

N (005 a )-7'L(a) ever, in this case the deflection coils consist of four coils 29, 31, 33 and 35 which are toroidally wound about the core. The various angular distances 0,, can be determined with reference to FIG. 3 in the same manner as for saddle-coils with reference to the FIG. 2. The calculation of the mean angular distance or, is also the same. The mean turns are denoted in FIG. 3by 37, 39, 41 and 43.

In FIG. 4 a subdivision into sections of the saddle coils of FIG. 2 is shown diagrammatically. By means of four'tappings (not shown) each of the two coils is divided into five sections 45, 47, 49, 51, 53 and 45, 47',

49, 51, 53', respectively. Each of these sections can be provided with a parallel circuit (not shown in FIG. 4). However, it appears to be particularly advantageous to provide one or more of the sections 45, 49 and 53 with a parallel circuit. The parallel circuit of the first section 45 and of the last section 53 can be utilized to influence the location of the mean turn 27. By reducing the impedance of the parallel circuit of section 45, the current flowing through this section is reduced. As regards the magnetic field which is generated by the coil this has the same effect as a reduction of the number of turns in this section and hence of the factors n(a) in the formula for u As these factors remain the same in the other sections, it is obvious that the value oz, increases as a result thereof. This means that the location of the mean turn is shifted in the direction of the last section 53. Similarly, a reduction of an impedance which is connected in parallel with section 53 will cause a shift of the mean turn 27 in the direction of the first section 45. The location of the mean turn 27 is of importance for the convergence on the entire display screen, whilst the convergence on the axes of the display screen is even determined substantially exclusively by this location. An optimum adjustment of the latter convergence can thus be obtained in the manner described above.

The convergence in the comer-s of the display screen is also dependent of the location of the mean turn 27. However, this convergence is also dependent of the manner in which the turns are distributed over the width of the coil. By influencing this distribution without changing the location of the mean turn 27 to any significant extent, optimum adjustment can be achieved of the convergence in the comers of the display screen without the already adjusted convergence on the axes being disturbed. To this end the section 49, extending on both sides of the mean turn, is also provided with a parallel circuit. If the impedance of this parallel circuit is varied, the factors n(a) in the formula for cos a vary for values of a,, which are slightly larger or smaller than a The overall effect of these variations on the value of a, is very slight, so that the location of the mean turn remains substantially the same. The turn distribution over the width of the coil, however, does change which can be clearly demonstrated by completely short-circuiting section 49. In that case the section no longer contributes to the magnetic field generated by the coil so that at this area an interruption is produced in the turns as if it were.

In a practical embodiment of saddle coils for a colour television display tube comprising three electron guns arranged on one line and having a deflection angle of 1 10, each of the coils comprising turns, each coil was divided by means of tappings such that each of the sections 45, 49 and 53 comprises ten turns. By providing these sections with parallel circuits and by varying the impedance thereof from zero to a value which is very large with respect to the impedance of each of the sections, it was found to be possible to correct convergence errors of 3 mm on the axes and of 5 mm in the comers of the display screen of the tube. I

During the winding of the coil it can be ensured that,

the mean turn 27 of the uncorrected coil is always shifted in one direction with respect to the desired location. In that case the mean turn 27 must always be displaced in the same direction upon correction, so that for this purpose only section 45 or only section 53 must be provided with a parallel circuit. That one of these two sections which is not used need not even exist as a separate section in that case, so that the relevant tapping can also be omitted.

So as to achieve a saving as regards the number of tappings, the sections 47 and 51 which are not provided with a parallel circuit can also be omitted. In that case the situation shown in FIG. 5 is obtained where the coil, in accordance with FIG. 1, is divided into only three sections 45, 49 and 53.

In the simplest case the coil is wound such that the mean turn is always shifted in the direction of, for example, section 53. In that case only one tapping is made, i.e. the tapping which limits section 53, and an impedance is connected parallel to section 53. Subsequently, the convergence in the corners and on the axes of the display screen is simultaneously adjusted by variation of this impedance. Obviously, this is possible only if this combined convergence adjustment constituted an acceptable compromise.

Using FIG. 2 as a basis, the division into sections has been described for saddle coils with reference to the FIGS. 4 and S. It is obvious that on the basis of FIG. 3 analogous figures for toroidal coils can be drawn which are subject to the same considerations. It is also possible to incorporate in one deflection coil system saddle coils for the deflection in the one direction and toroidal coils for the deflection in the other direction. This does not affect the above-mentioned considerations either.

The circuits which are connected parallel to the various sections preferably consist of variable resistors for the vertical deflection coils which are supplied with a deflection voltage of low frequency. For the horizontal deflection coils which are supplied with a deflection voltage of a much higher frequency, coils having a variable inductance are preferably used as the parallel circuit.

FIGS. 6 and 7 show some examples of circuits which can be used for deflection coil systems according to the invention.

FIG. 6a shows a pair of saddle-shaped horizontal deflection coils which are divided into sections 45, 47, 49, 51 and 53 and 45, 47', 49, 61' and 53, respectively. The coils are connected in series via a variable coil 55 which serves for compensation of mutual differences, and they are earthed in the centre of the series network. They are supplied from a known sawtooth gener ator 57. Connected in parallel to each of the sections 45, 49, 53, 45 49' and 53' is a coil having a variable inductance. These coils are denoted by 59, 61, 63, 59, 61' and 63, respectively.

FIG. 6b shows an analogous circuit for saddle-shaped vertical deflection coils. The sections are numbered in the same manner as in FIG. 6a. Connected in parallel with each of the sections 45, 49, 53, 45', 49' and 53 is a variable resistor. These resistors are denoted by 65, 67, 69, 65', 67' and 69, respectively. The assembly is supplied from a known sawtooth. generator 71. The voltage at the area of the centre of the series network can be adjusted by means of a potentiometer 73 which constitutes, on conjunction with the two fixed resistors 75 and 77, a voltage divider which is connected in parallel with the series network.

It appears from FIGS. 6a and 6b that, if the two deflection coils for one deflection direction are connected in series, a separate variable resistor or coil is required for each section provided with a parallel circuit. It appears that the number of variable resistors and coils can be reduced to one half by parallel connection of the deflection coils. This not only represents a saving as regards the number of components required for the circuit, but also the number of operations to be performed for adjustment is reduced.

FIGS. 7a and b show how such a circuit can be constructed for the horizontal and the vertical deflection coils, respectively. In both Figures each coil is again divided into five sections, the numbering of which corresponds to that in FIGS. 6a and b. Sections forming part of different coils are pairwise connected in parallel. As a result, the following pairs of sections are obtained: 45 and 53', 47 and 51', 49 and 49, 51 and 47'. 53 and 45. FIG. 7a shows that a coil having a variable inductance 79 is connected parallel to the first pair of sections 45, 53' of the horizontal deflection coils. Similarly, a variable coil 81 is connected parallel to the third pair of sections 49, 49', and a variable coil 83 is connected parallel to the fifth pair 53, 45. The complete parallel network is again supplied from the sawtooth generator 57 via a variable coil 85 for compensating differences between the two deflection coils.

FIG. 7b shows that a variable resistor 87 is connected parallel to the first pair of sections 45, 53 of the vertical deflection coils, a variable resistor 89 being connected parallel to the third pair 49, 49, and a variable resistor 91 being connected parallel to the fifth pair 53, 45'. Via a variable resistor 93 for the elimination of irregularities in the two deflection coils, the complete parallel network is again supplied by the sawtooth generator 71.

On the basis of the same considerations as described with reference to FIGS. 6 and 7 for saddle coils, it is also possible to demonstrate the desirability of pairwise parallel connection of sections forming part of different coils of the toroidal type.

What is claimed is:

1. A deflection coil system for a colour television display tube, comprising deflection coils for electron beam deflection in the horizontal and the vertical direction, respectively, each coil being a single coil and consisting of a number of turns of a conductive wire, each of the coils for at least one of the two deflection directions being divided into a number of seriesconnected sections in that at least one turn which is situated between the first and the last turn of the coil is provided with a tapping, characterized in that at least one of the sections of each of the coils for at least one deflection direction, is connected in parallel with a circuit means of adjustable impedance for adjusting the dynamic convergence.

2. A deflection coil system as claimed in claim 1, characterized in that at least the first (45) or the last (cos a )-n(a) id-M 4. A deflection coil system as claimed in claim 1,

characterized in that each of the sections provided with a parallel circuit comprises a number of turns substantially equal to one tenth of the total number of turns of the relevant coil. I

5. A deflection coil system as claimed in claim 1 characterized in that each of the parallel circuits (2]) of the horizontal deflection coils consists of a coil (59, 61, 63) of adjustable inductance, each of the parallel circuits (21) of the vertical deflection coils consisting of a variable resistor (65, 67, 69).

6. A deflection coil system as claimed in claim 1,

characterized in that sections (45, 53'; 49, 49; 53, 45') which form part of different coils are pair-wise connected in parallel.

7. A deflection coil system for a color television display tube,- comprising a pair of single deflection coils for electron beam deflection in the horizontal and the vertical directions respectively, each coil comprising a plurality of turns of a conductive wire, one of said coils having a tap dividing said one coil into a plurality of series-connected sections, and means parallel coupled to at least one of the sections of each of the coils for adjusting the dynamic convergence of the tube comprising an adjustable impedance element.

8. A deflection coil system as claimed in claim 7, wherein at least an end section of the relevant coils is provided with said parallel coupled impedance element.

9. A deflection coil system as claimed in claim 7, wherein a coil section which is provided with a parallel circuit extends on both sides of a mean turn, the angular distance a, between said mean turn and the deflection direction associated with this coil satisfying the formula:

(cos 0%)- n(a) in which n(a) represents the number of turns whose angular distance to the deflection direction amounts to a and N is the total number of turns of the coil.

10. A deflection coil system for a color television display tube, comprising a pair of single deflection coils for electron beam deflection in the horizontal and the vertical directions respectively, each coil comprising a plurality of turns of a conductive wire, one of said coils having a tap dividing said one coil into a plurality of series-connected sections, means parallel coupled to at least one of the sections of each of the coils for adjusting the dynamic convergence of the tube comprising an adjustable impedance element, and wherein one of said sections which is provided with a parallel circuit extends on both sides of a mean turn the angular distance a, between said mean turn and the deflection direction associated with this coil satisfying the formula:

(cos a )-n(a) cos (1,:

(cos u )-n(a) a and N is the total number of turns of the coil. 

1. A deflection coil system for a colour television display tube, comprising deflection coils for electron beam deflection in the horizontal and the vertical direction, respectively, each coil being a single coil and consisting of a number of turns of a conductive wire, each of the coils for at least one of the two deflection directions being divided into a number of seriesconnected sections in that at least one turn which is situated between the first and the last turn of the coil is provided with a tapping, characterized in that at least one of the sections of each of the coils for at least one deflection direction, is connected in parallel with a circuit means of adjustable impedance for adjusting the dynamic convergence.
 2. A deflection coil system as claimed in claim 1, characterized in that at least the first (45) or the last section (53) of the relevant coils is provided with a parallel circuit (21).
 3. A deflection coil system as claimed in claim 1, characterized in that a coil section (49) which is provided with a parallel circuit extends on both sides of a mean turn (27), the angular distance Alpha g between said mean turn (27) and the deflection direction associated with this coil satisfying the formula:
 4. A deflection coil system as claimed in claim 1, characterized in that each of the sections provided with a parallel circuit comprises a number of turns substantially equal to one tenth of the total number of turns of the relevant coil.
 5. A deflection coil system as claimed in claim 1, characterized in that each of the parallel circuits (21) of the horizontal deflection coils consists of a coil (59, 61, 63) of adjustable inductance, each of the parallel circuits (21) of the vertical deflection coils consisting of a variable resistor (65, 67, 69).
 6. A deflection coil system as claimed in claim 1, characterized in that sections (45, 53''; 49, 49''; 53, 45'') which form part of different coils are pair-wise connected in parallel.
 7. A deflection coil system for a color television display tube, comprising a pair of single deflection coils for electron beam deflection in the horizontal and the vertical directions respectively, each coil comprising a plurality of turns of a conductive wire, one of said coils having a tap dividing said one coil into a plurality of series-connected sections, and means parallel coupled to at least one of the sections of each of the coils for adjusting the dynamic convergence of the tube comprising an adjustable impedance element.
 8. A deflection coil system as claimed in claim 7, wherein at least an end section of the relevant coils is provided with said parallel coupled impedance element.
 9. A deflection coil system as claimed in claim 7, wherein a coil section which is provided with a parallel circuit extends on both sides of a mean turn, the angular distance Alpha g between said mean turn and the deflection direction associated with this coil satisfying the formula:
 10. A deflection coil system for a color television display tube, comprising a pair of single deflection coils for electron beam deflection in the horizontal and the vertical directions respectively, each coil comprising a plurality of turns of a conductive wire, one of said coils having a tap dividing said One coil into a plurality of series-connected sections, means parallel coupled to at least one of the sections of each of the coils for adjusting the dynamic convergence of the tube comprising an adjustable impedance element, and wherein one of said sections which is provided with a parallel circuit extends on both sides of a mean turn the angular distance Alpha g between said mean turn and the deflection direction associated with this coil satisfying the formula: 